From 22,000 Miles Up, This Satellite Tracks Airborne Health Threats Almost in Real Time

The new instrument, called TEMPO, captures hourly snapshots of the pollutants swirling in the daytime atmosphere over North America—“chemical weather” reports that are helpful to public health researchers and government officials

Virginia Gewin, Knowable Magazine

September 18, 2026 2:02 p.m.

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In early August, the skies above Portland, Oregon, took on an increasingly familiar sepia tint as easterly winds wafted plumes of gas and smoke from wildfires into the air over the city. At one point Portland’s air quality was ranked worst in the world, leading to the closure of summer camps and public pools and the cancellation of outdoor concerts. In a summer of intense heat and wildfires, similar scenarios played out in cities across North America—New York, Denver, Chicago, Toledo.

Above it all, a satellite recorded the dynamic swirl of gases and particulates fueling these air quality crises. From a vantage point 22,000 miles above the equator, the Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite, a joint effort by NASA and the Smithsonian Astrophysical Observatory, has provided near-real-time hourly snapshots of pollutants originating, migrating and dissipating in the daytime atmosphere over North America since September 2025.

Whereas previous pollution-monitoring satellites offered only one or two daily snapshots of air quality, this ongoing, continent-scale picture has helped researchers and regulators better understand and respond to some of the most unpredictable and uncontrollable pollutants in the atmosphere.

TEMPO reveals how pollution—like the weather—is not stagnant. “Pollution varies from hour to hour, from day to day,” says Laura Judd, a NASA research scientist at the Langley Research Center in Hampton, Virginia. “What we’re getting from TEMPO is this illustration of what we call ‘chemical weather.’”

Since the 1970 passage of the Clean Air Act, the United States has made tremendous progress reducing the levels of six common hazardous air pollutants that people breathe. But progress in reducing two pollutants in particular—ozone and particulates smaller than 2.5 micrometers in diameter, or PM2.5—has stalled over the past 15 years or so. Both are secondary pollutants, formed through chemical reactions in the atmosphere that are influenced by sunlight, heat and other variables.

With their complex chemistry and the fact that their precursors come from diffuse sources such as airports, agriculture and wildfires, secondary pollutants have been especially difficult to understand and control. They remain major contributors to the estimated 100,000 premature deaths, 10,000 premature births and 200,000 cases of child-onset asthma that are still caused each year by air pollution in the U.S. And as a 2023 paper in the Annual Review of Pharmacology and Toxicology concluded, there is growing evidence that air pollution may contribute to neurodevelopmental diseases such as schizophrenia as well as neurodegenerative diseases such as Alzheimer’s and Parkinson’s.

TEMPO’s ability to track how secondary pollutants form over the course of a day has wide-ranging potential to help reduce those figures. State and local governments can use TEMPO to identify and mitigate precursors, which helps them better comply with federal air quality standards. Scientists can create forecast models for secondary pollutants and issue timelier warnings of dangerous air quality. And public health researchers can inform pollution control measures with more precise information about where and when secondary pollutants affect human health.

TEMPO gathers data with a spectrometer that measures UV and visible light absorption patterns in the atmosphere, which can then be used to derive estimated concentrations of nitrogen dioxide (NO2), formaldehyde, aerosols and ground-level ozone down to a resolution of about four square miles. The satellite fills in the gaps left by the U.S. Environmental Protection Agency’s ground-based monitoring system, which provides high-quality data—but from only about one-third of the 3,000-plus U.S. counties.

“It is a game changer,” says Tracey Holloway, an atmospheric scientist at the University of Wisconsin-Madison who leads the NASA Health and Air Quality Applied Sciences Team and was a co-author of a 2021 Annual Review of Biomedical Data Science paper on satellite air quality monitoring. “It is going to really change our perception of who is breathing what.”

Where there’s smoke

Across North America this summer, that “what” has often been wildfire smoke. Especially in the western U.S., air quality districts perennially grapple with the outsize impacts of devastating wildfires. One study found that 23 percent of PM2.5 over the contiguous U.S. during late summer and early fall 2020 came from that year’s record-breaking wildfires. As a result, there were 3,720 exceedances of the EPA’s National Ambient Air Quality Standards, or NAAQS, the limits established for six key pollutants.

TEMPO is helping researchers demonstrate exactly how wildfire smoke from distant fires carries the precursors of secondary pollutants hundreds or thousands of miles, which helps air quality managers figure out when local sources are the culprit in a pollution spike and when they are not.

“In smoke plumes, there are always big blobs of formaldehyde,” says Shobha Kondragunta, a research physical scientist at the National Oceanic and Atmospheric Administration Center for Satellite Applications and Research in College Park, Maryland. That’s because, in the presence of sunlight, volatile organic compounds break down to form the chemical. Formaldehyde then reacts with nitrogen oxides in the atmosphere to produce ozone and PM2.5. TEMPO tracks both of these precursors.

The satellite also enables researchers to estimate smoke plume height, which can help them figure out how much sunlight is penetrating the haze and driving ozone formation in the ground-level air that people breathe.

TEMPO’s hourly high-resolution data also makes it easier to provide the documentation air agencies need to track wildfire smoke contributions to air quality, especially over long distances. That would help them avoid imposing unnecessary restrictions.

“We don’t want an area declared non-attainment because of wildfire smoke or dust storm events that a state will never be able to fix,” says Mary Uhl, executive director of the Western States Air Resources Council, a partnership among 15 Western state air agencies.

Amanda Fritz, an air pollution control engineer at the Connecticut Department of Energy and Environmental Protection in Hartford, says wildfire smoke plumes from hundreds of miles away in Canada this summer contributed to many, but not all, of the 13 ozone exceedances her state experienced by July 4 of this year—the earliest the region has reached this alarming milestone. Ozone has always been an issue in Connecticut because smog blows northeast from New York City. Even a little smoke can contribute just enough additional precursors to result in an ozone exceedance.

With TEMPO, we can identify “where ozone is being produced,” says Jennifer Kaiser, an air quality researcher at the Georgia Institute of Technology in Atlanta. “We’ve never measured near-surface ozone from a satellite before,” she adds. That information can point to key local sources of ozone precursors that can then be targeted by regulators.

Local sources

TEMPO has already helped air quality managers in Maryland understand how local ingredients are combining to create unhealthy air and prevent their jurisdictions from meeting air quality standards. For the first time in 2022, Maryland met all the NAAQS. But this year, the state had ten ozone exceedance days by August.

Given the tenuousness of the state’s success, Joel Dreessen, an air quality meteorologist with the Maryland Department of the Environment, used TEMPO to determine where blobs of ozone were coming from. Because ozone formation is intensified by high temperatures, Dreessen and colleagues compared TEMPO’s NO2 data on hot mornings with and without an ozone spike. They found that NO2 was a key determinant of local ozone formation, he says, and that its sources were industrial areas and the traffic-heavy Interstate 95 corridor.

With that knowledge, Dreessen can better forecast high-ozone events, and regulators and policymakers can identify policy solutions. He says TEMPO’s hourly observations were key to understanding how relatively cool air trapped near the ground in the morning accumulated a bubble of ozone precursors, which then drifted through the region on the day’s winds. “We were able to actually see how things are changing constantly in a day,” he says.

Making connections

This ability to watch things develop is invaluable in Mexico City, North America’s most populous city, set in a mountain valley that naturally traps air pollutants near the ground. Iván Gutiérrez-Avila, an instructor of environmental medicine at the Icahn School of Medicine at Mount Sinai in New York City, has found that TEMPO’s measurements of NO2 peak during the massive urban area’s morning rush hour. Prior to TEMPO, the best available satellite NO2 estimates provided a reading only once a day, in the early afternoon.

“If we use information that is not the most relevant for exposure, we will be missing important details for epidemiologic health models,” says Allan Just, Gutiérrez-Avila’s colleague at Mount Sinai and an environmental epidemiologist at Brown University in Rhode Island.

Further, Gutiérrez-Avila and Just have shown that emergency room visits increase during NO2 peaks, offering officials actionable information about the link between exposure and health impacts. “Communities need to be able to make decisions: Should we cancel the soccer match, move recess indoors or tell people to take protective actions outdoors?” Just says.

Making these decisions wisely can save lives. In Mexico, outdoor air pollution is estimated to cause about 1 in 17 deaths. Deaths and illness due to air pollution are estimated to have around $800 billion of economic impact annually in the United States, far exceeding the cost of much more visible threats like weather-related natural disasters.

With its ability to monitor some of the most pernicious air pollutants in the same way that meteorological satellites track natural hazards like tornadoes and hurricanes, the “chemical weather” satellite gives researchers and air quality managers a valuable new tool to reduce the impact of air pollution on hundreds of millions of lives.